Aspects of the invention can relate to a manufacturing method for a fine structure element, a fine structure element manufactured by the method, a spatial light modulator, and a projector. In particular, the invention can relate to a fine structure element, such as a micro-prism.
Related art dot matrix image display devices, such as a liquid crystal panel (a liquid crystal display device), a CRT display device, and a plasma display device are often used as image display devices. The dot matrix image display devices represent images with a large number of pixels periodically arranged two-dimensionally. In this case, so-called sampling noise is caused by this periodical arrangement structure and an image quality is deteriorated (an image looks rough). To cope with the problem, a method of reducing the deterioration in an image quality has been proposed. See, for example, JP-A-8-122709.
In the related art dot matrix image display devices, a light shielding section called a black matrix is provided in regions among the pixels in order to reduce unnecessary light. In recent years, a large screen is often observed from a relatively close distance as a form of using an image display device. Therefore, an observer may be conscious of an image of a black matrix. In the dot matrix image display devices in the past, an image quality is deteriorated as in an image with less smoothness, an image having roughness, or the like because of the image of the black matrix. For example, in JP-A-8-122709, it is difficult to reduce the deterioration in an image quality due to the image of the black matrix to improve an original image because of an influence of higher diffraction.
Therefore, it is conceivable to make light from the image display device incident on a prism group such that the observer is not conscious of the light shielding section of the black matrix or the like. A flat portion of the prism group transmits the light from the image display device directly. A refractive surface of the prism group refracts and transmits the light from the image display device. The light transmitted through the prism group generates light with an optical path thereof deflected on the refractive surface of the prism group in addition to light traveling straight after exiting from the flat portion. A pixel image can be formed on the black matrix by the light with the optical path thereof deflected. Consequently, the user is conscious of the black matrix less often.
A shape of respective prism elements forming the prism group is fine in the order of micrometer. In the related art, the prism elements of the fine shape are manufactured in a predetermined region by performing, for example, cutting using a cutting tool.
Usually, in the cutting using a cutting tool, a cutting tool having a desired shape is manufactured and prepared in advance. Then, the desired shape is obtained by cutting a member to be cut using this cutting tool. When the cutting tool is manufactured, it is possible to set an angle of the cutting tool by a unit of 0.1°. On the other hand, in the prism elements, it is desired that an angle formed by the flat surface and a slope serving as the refractive surface is in the order of one several hundredth, for example, 0.03°. Therefore, it is impossible to manufacture the cutting tool itself for manufacturing the prism elements.
Even when a microscope or the like is used, accuracy causing an error of about 3 μm is a limit of accuracy for a relative positional relation between a cutting object and a cutting tool, for example, a distance between the cutting tool and the cutting object and alignment concerning flatness (difference of elevation) of a surface of the cutting object. On the other hand, the prism elements are desired to be formed by cutting a substrate at a depth of 2 μm or less. Therefore, even if a machine tool, which performs cutting, is capable of controlling machining in the order of nanometer, the machine tool cannot perform machining for cutting the substrate at a depth of 2 μm or less accurately. Since it is extremely difficult to manufacture the prism elements of a fine shape, machining accuracy tends to be also determined by disturbances, such as temperature and the atmospheric pressure around the machine at the time of machining, temperature of the machine, wearing of the cutting tool, and the like. When fluctuation in the machining accuracy affects a shape of the prism elements, it is difficult to manufacture prism elements at high reproducibility. Therefore, in the cutting using the cutting tool, it is difficult to manufacture the prism elements in a desired prism shape.